﻿<p>The <em>IfcRelInterferesElements</em> objectified relationship
indicates that two elements interfere. Interference is a spatial
overlap between the two elements. It is a 1 to 1 relationship.
The concept of two elements interfering physically or logically
is described independently from the elements. The interference
may be related to the shape representation of the entities by
providing an interference geometry.</p>
<ul>
<li>When the interference geometry is available it can be passed
by the optional attribute <em>InterferenceGeometry</em> pointing to
<em>IfcConnectionGeometry</em>. The connection geometry is provided
as a point, curve, surface, or volume within the local placement
coordinate systems of the connecting elements. The
<em>IfcConnectionVolumeGeometry</em> is the default type to be used
for interference in 3D space, as indicated in e.g. clash
detections.</li>
<li>If the interference geometry is omitted then the interference
is provided as a logical relationship. Under this circumstance,
the connection point, curve, surface, or solid has to be
recalculated by the receiving application.</li>
</ul>
<p>The <em>RelatingElement</em> and <em>RelatedElement</em> define
the two elements in the relationship, that may have different
roles. This is controlled by the attribute
<em>ImpliedOrder</em>.</p>
<ul>
<li><em>ImpliedOrder</em>=TRUE  The <em>RelatingElement</em>
constitutes the primary element of the interference relationship.
If the interference is to be resolved by subtracting the
overlapping part, it should be subtracted from the
<em>RelatingElement</em>. The net result would be the
<em>RelatingElement</em> subtracted by the
<em>InterferenceGeometry</em>. This would be the case in
interference relationships where the <em>RelatedElement</em>
creates a void in the <em>RelatingElement</em> dynamically.</li>
<li><em>ImpliedOrder</em>=FALSE  The <em>RelatingElement</em> and
<em>RelatedElement</em> have no priority among each other. If the
interference is to be resolved then no information about whether
the <em>InterferenceGeometry</em> should be subtracted from the
<em>RelatingElement</em> or thed <em>RelatedElement</em> can be
traced. This would be the case for clash detection results.</li>
<li><em>ImpliedOrder</em>=UNKNOWN  No information about the
priorities is provided.</li>
</ul>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC4.
</blockquote>